The present invention relates to producing resist images employing compositions that act as negative photoresists. The present invention also relates to the resist images. The compositions according to the present invention do not require any additional photocatalysts, photoinitiators or added crosslinking agents. The negative photoresists are developable in water or an aqueous based composition.
One widely used method for forming a pattern such as metallic circuitry on a substrate in the manufacture of printed circuit boards in integrated circuits is to imagewise form a pattern of photoresist material over those areas of the substrate or over a metal-coated substrate to be shielded from metal deposition or metal removal. The photoresist layer is normally formed of a polymeric, organic material that is substantially unaffected by the metal deposition or metal removal process and, accordingly, protects the underlying areas.
The pattern is formed by imagewise exposing the photoresist material to irradiation through a photographic image, such as a glass master, by photolithographic techniques. The irradiations employed is usually X-ray, UV radiation, or electron beam radiation.
Photosensitive materials and/or compositions are either positive-acting (i.e. photosolubilizable) or negative-acting (i.e. photoinsolubilizable or photocrosslinkable). Positive-working (photo)sensitive compositions are rendered soluble (or developable) by actinic radiation (deep-near UV, x-ray or electron-beam) and can be removed using selective developing solutions leaving unexposed areas intact. Negative-working (photo)sensitive compositions are those which become insoluble upon exposure to actinic radiation. Selected solutions can dissolve and remove the unexposed areas of the composition while leaving the exposed portions intact. Development of such exposed materials yields negative tone images.
The majority of contemporary (photo)resist compositions for deep UV and e-beam applications are based on the principle of chemical amplification and consist of polymer matrixes, photoacid generators (PAG""s) and crosslinkers (for negative tone image generation). Photoacid generating onium salts are well known in the field of (photo)lithography. Useful (photo)catalysts include, for example, complexes of metal halides or salts of strong acids such as tetrafluoroborates, hexafluoroantimonates, and trifluorometanesulfonates, triphenylsulfonium triflate being an example; iodonium compounds such as t-butyl phenyl iodonium camphor sulfonate; hexafluoroarsenates and hexafluorophosphates. Although such (photo)resists show high (photo)speed and high resolution they develop some very serious lithographic and processing problems such as PAG diffusion (especially at high post-exposure bake temperatures, about 160xc2x0 C. used to process them), acid outgassing during exposure, very high sensitivity to airborne contamination by aminocompounds such as N-methylpyrrolidinone, contamination of coat tracks and masks, process time delay dependence and limited shelf life.
Reiser (see, xe2x80x9cPhotoreactive Polymers. The Science and Technology of Resistsxe2x80x9d, p. 22, p. 258, p. 311, John Wiley and Sons, NY (1989)) describes the background of negative tone (photo)resist materials which are based on the principle of photoinduced polarity changes in polymer-bound functional groups such as poly(vinyl cinnamate), poly(vinyl cinnamylide acetate), chalcones, phenyldiacrylates attached by an esterlinkage to poly(vinyl alcohol) or incorporated in the backbone of a polyester as well as methacrylic copolymers with dimethylmaleimide or diphenylcyclopropene pendant chromophore groups; negative resists based on nitrene chemistry which are prepared by attaching azido groups to a polymer chain; systems based on bis-azides or 4-azidochalcones. Negative systems based on macroradical coupling reactions (photocrosslinking of copolymers containing benzophenone and p-dimethylamino-phenyl groups) as well as negative tone resists based on photoinduced polarity change are also discussed.
W. E. Feely et al., (see Proceedings of the 7th International Conference on Photopolymers, SPE, 49 (1985)) discusses the use of melamine crosslinkers to form negative tone images without the use of photocatalysts.
U.S. Pat. No. 4,284,707 describes negative working material based on crosslinking of two copolymers without onium salts.
U.S. Pat. No. 4,603,195 (1986) describes negative tone organosilicon photoresist based on 2,1,5-naphthoquinone diazo chemistry. Also J. M. Shaw and M. Hatzakis demonstrated that some commercial positive tone novolac photoresists based on diazoquinone chemistry work as negative tone base developable e-beam resists with high resolution and sensitivity (see J. M. Shaw and M. Hatzakis, IEEE Trans. Electron Devices, vol. ED-25, 425 (1978)).
Negative tone e-beam resists have been developed on the basis of polymeric materials containing glycidyl methacrylate units (see T. Hiraeti et al. J. Electrochem. Soc., vol. 118, 669 (1971); Y. Taniguchi et al., J. Appl. Phys. vol. 18, 1143 (1979); L. F. Thompson et al. J. Vac. Sci. Technol. vol. 12, 1280 (1975)).
Copolymers of allyl- and propargyl methacrylates with 2-hydroxyethylmethacrylate have been found to work as sensitive negative tone e-beam resist materials (see Z. C. H. Tan et al., Proc. SPIE, vol. 461, 135 (1984) and R. C. Daly et al., Proc. SPIE, vol. 539, 138 (1985)).
A series of relatively effective negative tone solvent developable e-beam resists with a good plasma stability was developed using polystyrene type copolymers containing chloro-, iodo- or chloromethyl groups in the p-position in aromatic ring (see J. Luitkis et al., SPE Reg. Tech. Conf., Ellenville, N.Y., p. 223 (1982); H. S. Choong et al., J. Vac. Sci. Technol. vol. 19, 1121 (1981)). Similar results are achievable by quarternization of poly(vinyl pyridine) with methyl iodide (see K. I. Lee et al., Polym. Bull., vol. 10, 39 (1983)).
Some other examples of negative tone deep UV resists are as follows:
CGR-chemically amplified resist based on poly(p-hydroxystyrene)or its copolymers with styrene or vinylcyclohexane with powderlink crosslinker and a PAG.
SNR-(Shipley Negative Resist) is based on poly(p-hydroxystyrene), a melamine crosslinker and a PAG.
ZEP-520 and ZEP-7000 are conventional chain scission positive tone solvent developable resist formulations (Nippon Zeon Co., Ltd.).
KRS is a chemically amplified positive tone resist based on ketal chemistry (see O. M. Tanenbaum et al., J. Vac. Sci. Technol. B 14(6), 3829 (1996)).
Even though a number of photoresist materials are known and are capable of forming desired masking patterning providing negative tone compositions which exhibit acceptable imaging (resolution and sensitivity) characteristics to be suitable as an image or pattern mask, especially for integrated circuits, along with being developable in water and being not chemically amplified is quite unusual. As discussed above, various problems are encountered with chemically amplified photoresists including certain contamination damages, process time delay dependence and limited shelf life.
The present invention provides for achieving a patterned negative tone photoresist without requiring any additional photocatalysts or photoinitiators. Moreover, the present invention makes it possible to fabricate a patterned negative tone photoresist without requiring the addition of individual polyfunctional compounds acting as crosslinking agents.
The present invention provides for fabricating a patterned negative photoresist engaging certain materials that contain a component that permits crosslinking. The present invention makes it possible to employ non-chemically amplified materials.
In particular, the present invention relates to a method for forming a pattern of a negative photoresist which comprises:
a) providing on a substrate a layer of a negative photoresist composition comprising a polymer having at least one recurring group represented by the formula 1: 
wherein
R=H, CH3xe2x80x94, alkyl-, or xe2x80x94CH2SiMe3;
Rxe2x80x2=xe2x80x94(CH2CH2O)mRxe2x80x3,
-alkyl, cycloalkyl, or aryl, wherein Rxe2x80x3 is alkyl, cycloalkyl or aryl; and wherein typically m is an integer of 1 to about 10 and n is typically an integer of 5 to about 104;
b. imagewise exposing the layer to irradiation; and
C. developing the photoresist by removing portions of the layer not exposed to thereby form the pattern.
The present invention also relates to the patterned negative photoresist obtained by the above process.
Another aspect of the present invention relates to a structure comprising a substrate and a layer of a patterned negative photoresist on the substrate wherein the patterned negative photoresist is obtained by crosslinking a polymer having at least one recurring group represented by the formula 1 above.